A dockable computer system includes a portable computer unit, usually a notebook or laptop, and a stationary or base computer unit having a docking station for receiving the portable computer unit. Dockable computer systems may be operated in a docked state, in which both computer units are physically associated as a generally unified system, or the remote unit may be separated from its host for independent operation in an undocked state.
Rudimentary docking systems of the foregoing variety have been designed in an effort to meet the needs of today's mobile computer users for "ubiquitous" computing system capabilities, to fulfill their computing needs in diverse aspects of their professional and personal lives and in sundry locations. Contemporary dockable computer systems approach this problem through a single system having a detachable mobile computing component or subsystem.
The expandable desktop computer provides greater storage resources, network connectivity, larger displays, and other superior facilities which are necessary for the typical range of generally demanding home and office computing. The portable computer (mobile computer unit) allows the user to have computing capabilities while outside the home or office by detaching that component with its indigenous hardware and resident software. The computing capabilities of the portable computer are somewhat limited due to size, weight and power constraints but represent the best available approach in these embryonic attempts to balance portable mobility needs.
When the user leaves the host environment of home or office, the portable computer is undocked (that is, physically detached) from the docking station of the stationary computer unit. Applications, files, and other data needed for the mobile computing task must have previously been stored in the portable computer. When the user returns to the host environment, the portable computer is reunited (docked) with the docking station so the applications, the files and other data are stored and maintained in a single location. Thus, the use of a dockable computer system allows the user to have access to any needed applications, files and other data just before embarking on the mobile computing task.
When the dockable computer system changes from the undocked state to the docked state or the docked state to the undocked state (a docking event), protective measures are required to prevent catastrophic failures caused by physically connecting or disconnecting the active buses of the portable computer and the docking station. For example, the bus of the portable computer can be referenced to a substantially different ground level or signal level than the bus of the docking station. Connecting these buses can cause large inrushes of current, especially through the ground conductors, and signal overdrive conditions. Large inrushes of current and signal overdrive conditions may cause component damage and excessive battery wear or deterioration. Also, bidirectional terminals on the portable computer and bidirectional terminals on the docking station may be inappropriately set to both be in an input state or to both be in an output state. Such a situation can cause input leakages (resulting in excessive battery wear) and signaling failures.
Contemporary dockable computer systems are typically "cold docking" systems which protect the buses only by powering off the portable computer and docking station, rendering the buses inactive so protective measures are not required. These "cold docking" systems are disadvantageous because the user must wait for the dockable computer system to be turned on, rebooted, and reconfigured before the dockable computer system is operational in the docked state. These systems are inconvenient because of the amount of time required to change from the docked state to the undocked state or from the undocked state to the docked state.
There is a need for a "hot docking" computer system and a "warm docking" computer system. A "hot docking" computer system as envisioned herein is a dockable computer system which can change states with the portable computer running at full power. A "warm docking" system may be thought of as a dockable computer system which can change when the portable computer is in a reduced power state when the portable computer is not running at full power. Examples of the reduced power state are the suspend state and standby state now incorporated in some microprocessor systems. Hot docking and warm docking systems advantageously enable the user to more immediately begin computer tasks because the systems are powered on throughout the docking event.
Thus, there is a need for a dockable computer system which includes circuitry that allows the dockable computer system to change states while powered on. More particularly, there is a need for a dockable computer system which drives the active buses of the portable computer and docking station to a dockable state or a docking safe state when the system is docked or undocked.